Quite a bit of work has been done in continuous casting mold fluxes as indicated by the numerous patents that have been issued pertaining thereto. See my copending patent application Ser. No. 874,024 entitled "Continuous Casting Mold Flux Powders" filed Feb. 1, 1978. While there is no denying the importance of the proper mold flux for successful continuous casting, the flux or slag over the molten metal in the tundish can also be very important. This is especially the case where aluminum-killed steel is being cast and the aluminum is added to the steel at the ladle prior to teeming in the tundish. This invention relates to an improved flux for tundishes, especially for use with aluminum-killed steel.
The primary purpose for using a tundish flux is to scavenge deoxidation products from aluminum-killed steel and to fluidize the viscous and refractory almunia-enriched slags which form and accumulate on the surface of steel being teemed in the tundish as successive heats are continuous cast. Additionally, a tundish flux is used to minimize or eliminate slag build up on tundish sidewalls with minimal corrosion of alumina refractories or silica sideboards. Also, during the late stages of the last heat being cast, a tundish flux is used to fluidize the accumulated slag sufficiently to assure complete draining of the tundish. At tundish operating temperatures of about 2800.degree. F., a tundish flux must exhibit rapid fusion and spread, very high fluidity and a high alumina solubility.
One problem with introducing powders to the tundish is the tundish is often very unaccessible and may be ten feet or more below the point where the tundish flux powder can be introduced. Powder materials packed in polyethylene or paper bags will blow-out of the tundish as soon as the bag is ignited. Blow-out is caused by hot air currents rising from the tundish and results in smoking and dusting over the tundish. Also it is unfortunate that bagged material does not lend itself to automated and semi-automated feeding.
By way of comparison, it should be noted that fluxes are used in a number of processes, for example, in fluid mold casting and ingot mold casting as illustrated by U.S. Pat. Nos. 3,993,474 and 3,567,432. The powders disclosed in these patents have some compositional similarities with the tundish fluxes disclosed herein.